Hot stamping component and method of manufacturing the same

ABSTRACT

Disclosed is a hot-stamping component, which includes a base steel plate; and a plated layer on the base steel plate and including a first layer, a second layer, and an intermetallic compound portion having an island shape in the second layer, wherein the first layer and the second layer are sequentially stacked, and an area fraction of the intermetallic compound portion with respect to the second layer is an amount of 20% to 60%.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119to Korean Patent Application No. 10-2019-0171790, filed on Dec. 20,2019, and No. 10-2020-0126391, filed on Sep. 28, 2020, in the KoreanIntellectual Property Office, the disclosures of which are incorporatedby reference herein in their entirety.

BACKGROUND 1. Field

The present invention relates to a hot-stamping component and a methodof manufacturing the same.

2. Description of the Related Art

As environmental regulations and fuel economy-related regulations arestrengthened all over the world, the need for lighter materials forvehicles is increasing. Accordingly, researches on and development ofultra-high-strength steel and hot-stamping steel have been activelyconducted. A hot stamping process generally includesheating/molding/cooling/trimming operations, and uses a phasetransformation of materials and a change in microstructures during theprocess.

Recently, studies have been actively conducted to prevent the occurrenceof delayed fracture that occurs in a hot-stamping component manufacturedby a hot stamping process as well as to improve the corrosion resistanceand weldability of the same. Related technologies include a KoreanPatent Publication No. 10-2018-0095757 directed to a method ofmanufacturing a hot-stamping component.

SUMMARY

Exemplary embodiments of the present disclosure provide a hot-stampingcomponent with improved hydrogen embrittlement, corrosion resistance,and weldability, and a method of manufacturing the hot-stampingcomponent.

According to an exemplary embodiment of the present disclosure, providedis a hot-stamping component, which includes a base steel plate; and aplated layer on the base steel plate and including a first layer, asecond layer, and an intermetallic compound portion having an islandshape in the second layer, wherein the first layer and the second layerare sequentially stacked, and an area fraction of the intermetalliccompound portion with respect to the second layer is 20% to 60%.

According to the exemplary embodiment, the second layer may include atleast one of an FeAl₃ phase and an Fe₂Al₅ phase, and an average grainsize of the FeAl₃ phase and the Fe₂Al₅ phase is 3 μm to 15 μm.

According to the exemplary embodiment, the intermetallic compoundportion may be discontinuously arranged in the second layer.

According to the exemplary embodiment, the intermetallic compoundportion may include an amount of 62 wt % to 67 wt % of iron (Fe), anamount of 2 wt % to 6 wt % of silicon (Si), and an amount of 30 wt % to34 wt % of aluminum (Al).

According to the exemplary embodiment, a content of aluminum in theintermetallic compound portion may be greater than a content of aluminumin the second layer.

According to the exemplary embodiment, the plated layer may furtherinclude a surface layer stacked on the second layer, and an averagethickness of the surface layer may be about 100 nm to about 200 nm.

According to the exemplary embodiment, the base steel plate may includean amount of 0.19 wt % to 0.38 wt % of carbon (C), an amount of 0.1 wt %to 1 wt % of silicon (Si), an amount of 1 wt % to 2 wt % of manganese(Mn), an amount of greater than 0 wt % and less than or equal to 0.03 wt% of phosphorus (P), an amount of greater than 0 wt % and less than orequal to 0.01 wt % of sulfur (S), an amount of 0.1 wt % to 0.6 wt % ofchromium (Cr), an amount of 0.01 wt % to 0.05 wt % of titanium (Ti), anamount of 0.001 wt % to 0.005 wt % of boron (B), remaining iron (Fe),and unavoidable impurities.

According to another exemplary embodiment of the present disclosure,provided is a method of manufacturing a hot-stamping component, whichincludes manufacturing a plated steel plate by immersing a base steelplate in a plating bath including aluminum and silicon; coating theplated steel plate with an oil including an ester-based compound;forming a blank by cutting the plated steel plate coated with the oil;and heating the blank in a heating furnace.

According to the exemplary embodiment, the oil may be coated at 0.1 g/m²to 10 g/m² on the plated steel plate.

According to the exemplary embodiment, the oil may include an amount of10 wt % to 30 wt % of hydrotreated heavy paraffin refined oil, an amountof 30 wt % to 50 wt % of solvent-dewaxed heavy paraffin refined oil, anamount of 1 wt % to 5 wt % of solvent-refined heavy paraffin refinedoil, and an amount of 10 wt % to 40 wt % of an ester-based compound.

According to the exemplary embodiment, in the heating of the blank inthe heating furnace, the heating furnace may have a plurality ofsections having different temperature ranges from each other, and theblank may be heated in stages in the heating furnace.

According to the exemplary embodiment, in the heating of the blank inthe heating furnace, a heating rate of the blank may be 4.5° C./s to 10°C./s.

According to the exemplary embodiment, in the heating of the blank inthe heating furnace, at least two blanks having different thicknessesfrom each other may be simultaneously transferred into the heatingfurnace.

According to the exemplary embodiment, the method may further include,after the heating of the blank, transferring the heated blank from theheating furnace to a press mold; forming a molded body by hot-stampingthe transferred blank; and cooling the formed molded body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a hot-stamping component accordingto an exemplary embodiment;

FIG. 2 is a table showing an evaluation result of the peeling resistanceof a second layer included in a hot-stamping component according to anexemplary embodiment;

FIG. 3 is a schematic flowchart illustrating an operation of preparing ablank used in a method of manufacturing a hot-stamping componentaccording to an exemplary embodiment;

FIG. 4 is a schematic flowchart illustrating a method of manufacturing ahot-stamping component according to an exemplary embodiment;

FIG. 5 is a diagram for explaining a blank heating operation of FIG. 3 ;

FIG. 6 is a graph showing a change in temperature over time of a blankcoated with an oil including an ester-based compound and a blank coatedwith a general oil;

FIGS. 7A to 7C are graphs respectively showing heating degassinganalysis results of Embodiment 1 and Comparative Example 1, Embodiment 2and Comparative Example 2, and Embodiment 3 and Comparative Example 3;

FIGS. 8A and 8B are photographs respectively showing a surface layer ofEmbodiment 1 and Comparative Example 1;

FIG. 9 is a graph showing resistance measurement results of hot-stampingcomponents according to Embodiment 1 and Comparative Example 1 duringspot welding; and

FIG. 10 is a graph showing corrosion evaluation experiment results ofEmbodiment 1 and Comparative Example 1.

DETAILED DESCRIPTION

As the present disclosure allows for various changes and numerousembodiments, particular embodiments will be illustrated in the drawingsand described in detail in the written description. Effects, features,and methods of achieving the same of the present disclosure aredescribed in detail below with drawings. This present disclosure may,however, be embodied in many different forms and should not be construedas being limited to the exemplary embodiments set forth herein.

In the following exemplary embodiments, such terms as “first,” “second,”etc., may be used to describe various components and to distinguish onecomponent from the other component, such components must not be limitedto the above terms.

An expression used in the singular encompasses the expression of theplural, unless it has a clearly different meaning in the context.

In the following embodiments, it is to be understood that the terms suchas “including,” “having,” and “comprising” are intended to indicate theexistence of the features, numbers, steps, actions, components, parts,or combinations thereof disclosed in the specification, and are notintended to preclude the possibility that one or more other features,numbers, steps, actions, components, parts, or combinations thereof mayexist or may be added.

It will be understood that when a layer, region, or component isreferred to as being “formed on” another layer, region, or component, itcan be directly or indirectly formed on the other layer, region, orcomponent.

Sizes of components in the drawings may be exaggerated or reduced forconvenience of explanation. In other words, since sizes and thicknessesof components in the drawings are arbitrarily illustrated forconvenience of explanation, the following embodiments are not limitedthereto.

When a certain embodiment may be implemented differently, a specificprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order.

Hereinafter, the present disclosure will be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the inventive concept are shown. Likewise reference numerals maydenote like elements in different drawings.

FIG. 1 is a cross-sectional view of a hot-stamping component 10according to an embodiment of the present disclosure.

Referring to FIG. 1 , the hot-stamping component 10 according to anexemplary embodiment of the present disclosure may include a base steelplate 100 and a plated layer 200 on the base steel plate 100.

The base steel plate 100 may be a steel plate manufactured by performinga hot-rolling operation and a cold-rolling operation on cast steel slabsto include a certain alloying element in a certain content. For example,the base steel plate 100 may include carbon (C), silicon (Si), manganese(Mn), phosphorus (P), sulfur (S), titanium (Ti), boron (B), remainingiron (Fe), and other unavoidable impurities. In addition, the base steelplate 100 may further include one or more components of niobium (Nb),molybdenum (Mo), and aluminum (Al).

C is a major element that determines strength and hardness of the basesteel plate 100, and is added to secure tensile strength andhardenability characteristics of the base steel plate 100 after a hotstamping operation. For example, an amount of 0.19 wt % to 0.38 wt % ofC may be included based on a total weight of the base steel plate 100.When a content of C is less than 0.19 wt %, the mechanical strength ofthe base steel plate 100 may be difficult to be secured. On the otherhand, when the content of C exceeds 0.38 wt %, the toughness of the basesteel plate 100 may be reduced or a problem of brittleness control maybe caused.

Si is a solid solution strengthening element, which may improve strengthand ductility of the base steel plate 100. In addition, Si may suppressthe formation of cementite, which is a starting point of crack due tohydrogen embrittlement. Based on the total weight of the base steelplate 100, an amount of 0.1 wt % to 1 wt % of Si may be included. When acontent of Si is less than 0.1 wt %, the above-described effect may bedifficult to obtain. On the other hand, when the content of Si exceeds 1wt %, the plating characteristics of the base steel plate 100 may bereduced.

Mn is added to increase hardenability and strength of the base steelplate 100 during heat treatment. Based on the total weight of the basesteel plate 100, an amount of 1 wt % to 2 wt % of Mn may be included.When a content of Mn is less than 1 wt %, a grain refining effect maynot be sufficient, and the hard phase fraction of a hot-stampingcomponent may be insufficient. On the other hand, when the content of Mnexceeds 2 wt %, the ductility and toughness of the base steel plate 100due to manganese segregation or perlite bands may be reduced, which maycause a decrease in bending performance of the base steel plate 100 anda heterogeneous microstructure may occur.

P is added to prevent toughness of the base steel plate 100 fromreducing. Based on the total weight of the base steel plate 100, anamount of greater than 0 wt % and less than or equal to 0.03 wt % of Pmay be included. When a content of P exceeds 0.03 wt %, an ironphosphide compound is formed to reduce toughness of the base steel plate100, and cracks may be caused in the base steel plate 100 during amanufacturing operation.

Based on the total weight of the base steel plate 100, an amount ofgreater than 0 wt % and less than or equal to 0.03 wt % of S may beincluded. When a content of S exceeds 0.01 wt %, hot-workability of thebase steel plate 100 may be reduced, and surface defects such as cracksmay occur due to the formation of large inclusions.

Chromium (Cr) is added to improve hardenability and strength of the basesteel plate 100. Based on the total weight of the base steel plate 100,an amount of 0.1 wt % to 0.6 wt % of Cr may be included. When a contentof Cr is less than 0.1 wt %, an effect of improving the hardenabilityand strength of the base steel plate 100 may not be sufficient. On theother hand, when the content of Cr exceeds 0.6 wt %, production cost mayincrease and the toughness of the base steel plate 100 may decrease.

Titanium (Ti) is added to enhance hardenability of the base steel plate100 by forming precipitates after a hot-stamping heating treatment, andimprove materials of the base steel plate 100. In addition, Ti forms aprecipitated phase such as Ti(C, N) or the like at a high temperature,thereby effectively contributing to refinement of austenite grains.Based on the total weight of the base steel plate 100, an amount of 0.01wt % to 0.05 wt % of Ti may be included. When a content of Ti is lessthan 0.01 wt %, the formation of precipitates is insignificant and thegrain refining effect may not be sufficient. On the other hand, when thecontent of Ti exceeds 0.05 wt %, an elongation percentage of the basesteel plate 100 may be decreased and a decrease in toughness of the samemay occur.

Boron (B) is added to secure hardenability and strength of the basesteel plate 100 by obtaining a martensitic structure. B also has a grainrefining effect by increasing an austenite grain growth temperature.Based on the total weight of the base steel plate 100, an amount of0.001 wt % to 0.005 wt % of B may be included. When a content of B isless than 0.001 wt %, an effect of improving the hardenability of thebase steel plate 100 may not be sufficient. On the other hand, when thecontent of B exceeds 0.005 wt %, the risk of brittleness and the risk oflow elongation percentage of the base steel plate 100 may increase.

For example, when the tensile strength of a manufactured hot-stampingcomponent is aimed at 1680 MPa or more, the base steel plate 100 mayinclude an amount of 0.20 wt % to about 0.50 wt % of C, an amount of0.15 wt % to 0.70 wt % of Si, an amount of 0.5 wt % to 2.0 wt % of Mn,an amount of greater than 0 wt % and less than or equal to 0.05 wt % ofP, an amount of greater than 0 wt % and less than or equal to 0.01 wt %of S, remaining iron (Fe), and other unavoidable impurities.Alternatively, the base steel plate 100 may include one or more of anamount of 0.001 wt % to 0.005 wt % of B, an amount of 0.05 wt % to 0.5wt % of Cr, an amount of 0.05 wt % to 0.3 wt % of molybdenum (Mo), andan amount of 0.05 wt % to 0.6 wt % of nickel (Ni). In addition, the basesteel plate 100 may include one or more of titanium (Ti), niobium (Nb),and vanadium (V) in an amount of greater than 0 wt % and less than orequal to 0.1 wt %.

The plated layer 200 is formed to a thickness of 10 μm to 50 μm on atleast one surface of the base steel plate 100, and includes Al. Herein,the thickness of the plated layer 200 may mean an average thickness ofthe plated layer 200 over an entire area of the plated layer 200. Whenthe thickness of the plated layer 200 is less than 10 μm, the corrosionresistance of the base steel plate 100 (or the hot-stamping component10) may be reduced, and when the thickness of the plated layer 200exceeds 50 μm, the productivity of the hot-stamping component 10 maydecrease, and the plated layer 200 may be attached to a roller or a moldduring a hot stamping operation, and thus the plated layer 200 may bepeeled off from the base steel plate 100.

The plated layer 200 may include a first layer 210 and a second layer220 which are sequentially stacked on the base steel plate 100. Inaddition, the plated layer 200 may further include a surface layer 240stacked on the second layer 220. The surface layer 240 is a layerincluding an amount greater than or equal to 80 wt % of Al, and the basesteel plate 100 may be prevented from being oxidized by arranging thesurface layer 240 on the base steel plate 100. For example, an averagethickness of the surface layer 240 on the base steel plate 100 may be100 nm to 500 nm.

The first layer 210 and the second layer 220 may be formed ofpolycrystalline. For example, the thickness of the second layer 220 maybe formed greater than that of the first layer 210. For example, thethickness of the second layer 220 may be greater than the thickness ofthe first layer 210 by 1.6 times to 3.6 times. In a method ofmanufacturing a hot-stamping component to be described below, the platedlayer 200 may be formed, by a thermal reaction in a blank heatingoperation of a hot stamping operation, as an Fe—Al-based plated layer inwhich Si is finally dissolved.

The plated layer 200 may include the first layer 210 on the base steelplate 100. The first layer 210 may include Fe, Al, and Si which aremixed with each other by heat diffusion during the hot stampingoperation. For example, the first layer may have an α-Fe phase or anFe₃Al₂ phase. Also, the first layer 210 may further include a void.

The plated layer 200 may include the second layer 220 on the first layer210. In addition, the plated layer 200 may further include anintermetallic compound portion 230 in the second layer 220 in an islandshape. The second layer may include at least one of an FeAl₃ phase andan Fe₂Al₅ phase, and an average grain size of the FeAl₃ phase and theFe₂Al₅ phase may be 3 μm to 15 μm.

FIG. 2 is a diagram showing an evaluation result of peeling resistanceof a second layer included in a hot-stamping component according to anembodiment. In detail, FIG. 2 is a diagram showing a result ofmeasuring, through a dolly test, a strength at which the second layer220 is peeled off from the base steel plate 100.

Referring to FIG. 2 , when an average grain size of the second layer 220is 3 μm (in case a), an adhesive strength thereof is 6.52 MPa, when theaverage grain size of the second layer 220 is 7 μm (in case b), theadhesive strength thereof is 6.09 MPa, when the average grain size ofthe second layer 220 is 10 μm (in case c), the adhesive strength thereofis 5.37 MPa, and when the average grain size of the second layer 220 is15 μm (in case d), the adhesive strength thereof is 5.21 MPa. Inaddition, when the average grain size of the second layer 220 is 17 μm(in case e,) the adhesive strength thereof is 3.94 MPa, and when theaverage grain size of the second layer 220 is 20 μm (in case f,) theadhesive strength thereof is 3.85 MPa. Accordingly, it can be seen thatwhen the average grain size of the second layer 220 exceeded 15 μm, theadhesive strength of the second layer 220 was lowered.

Therefore, when the average grain size of the second layer 220 exceeds15 μm, the plated layer 200 may be easily peeled off from the base steelplate 100. In detail, as the adhesive strength of the second layer 220is lowered when the average grain size of the second layer 220 exceeds15 μm, the second layer 220 may be easily peeled off from the base steelplate 100 and/or the first layer 210.

Also, when using a method of manufacturing a hot-stamping component tobe described below, it may be difficult to form an average grain size ofless than 3 μm.

Accordingly, when the average grain size of the second layer 220satisfies 3 μm to 15 μm, an adhesive strength of the plated layer 200including the second layer 220 may be improved, and the peelingresistance of the plated layer 200 may be improved.

The intermetallic compound portion 230 may be in the second layer 220.The intermetallic compound portion 230 may be distributed in the secondlayer 220 in an island shape. The intermetallic compound portion 230 maybe discontinuously arranged in the second layer 220. The weldability andthe peeling resistance of a hot-stamping component may be improved byarranging the intermetallic compound portion 230 in the second layer 220in an island shape.

Each intermetallic compound portion 230 discontinuously arranged in thesecond layer 220 may have a size of 1 μm to 5 μm. The intermetalliccompound portion 230 may be distributed in a fraction of 20% to 60% withrespect to a total cross-sectional area of the second layer 220. Thatis, an area fraction of the intermetallic compound portion 230 withrespect to the second layer 220 may be 20% to 60%. When using the methodof manufacturing a hot-stamping component to be described below, it isdifficult to form the area fraction of the intermetallic compoundportion 230 with respect to the second layer 220 to less than 20%. Whenthe area fraction of the intermetallic compound portion 230 with respectto the second layer 220 exceeds 60%, the weldability of the hot-stampingcomponent may decrease.

The intermetallic compound portion 230 may include an Fe—Al compound,and a content of Al included in the intermetallic compound portion 230may be greater than a content of Al included in the second layer 220.

For example, the first layer 210 may include an amount of 82 wt % to 90wt % of Fe, an amount greater than 0 wt % and less than or equal to 5 wt% of Si, and about 9 wt % to about 15 wt % of Al, the second layer 220may include an amount of 39 wt % to 47 wt % of Fe, an amount greaterthan 0 wt % and less than or equal to 2 wt % of Si, and an amount of 53wt % to 61 wt % of Al, and the intermetallic compound portion 230 mayinclude an amount of 62 wt % to 67 wt %, an amount of 2 wt % to 6 wt %of Si, and an amount of 30 wt % to 34 wt % of Al.

FIG. 3 is a schematic flowchart illustrating a method of manufacturing ahot-stamping component according to an exemplary embodiment of thepresent disclosure, and FIG. 4 is a schematic flowchart illustrating anoperation of manufacturing a plated steel plate of FIG. 3 . Hereinafter,the method of manufacturing a hot-stamping component will be describedwith reference to FIGS. 3 and 4 .

Referring to FIG. 3 , the method of manufacturing a hot-stampingcomponent according to an exemplary embodiment may include a platedsteel plate manufacturing operation S110, an oil coating operation S120,a blank forming operation S130, a blank heating operation S140, a blanktransferring operation S150, a molded body forming operation S160, and amolded body cooling operation S170.

For example, the method of manufacturing a hot-stamping component mayinclude the oil coating operation S120, the blank forming operationS130, the blank heating operation S140, the blank transferring operationS150, the molded body forming operation S160, and the molded bodycooling operation S170.

For example, in the method of manufacturing a hot-stamping component,the oil coating operation S120 may be performed after the blank formingoperation S130 is performed. That is, the method of manufacturing ahot-stamping component may be performed in an order of the blank formingoperation S130, the oil coating operation S120, the blank heatingoperation S140, the blank transferring operation S150, the molded bodyforming operation S160, and the molded body cooling operation S170.

As shown in FIG. 4 , the plated steel plate manufacturing operation S110may include a hot-rolling operation of a steel slab S210, acooling/coiling operation S220, a cold-rolling operation S230, anannealing heat treatment operation S240, and a hot-dip plating operationS250.

First, a half finished steel slab, which is a target of an operation offorming a plated steel plate, is prepared. At this time, the steel slabmay include an amount of 0.19 wt % to 0.38 wt % of C, an amount of 0.1wt % to 1 wt % of Si, an amount of 1 wt % to 2 wt % of Mn, an amount ofgreater than 0 wt % and less than or equal to 0.03 wt % of P, an amountof greater than 0 wt % and less than or equal to 0.01 wt % of S, anamount of 0.1 wt % to 0.6 wt % of Cr, an amount of 0.01 wt % to 0.05 wt% of Ti, an amount of 0.001 wt % to 0.005 wt % of B, remaining Fe, andunavoidable impurities.

A reheating operation is performed on the steel slab for hot-rolling. Inthe operation of reheating the steel slab, segregated components, duringcasting, are re-used by reheating the steel slab secured through acontinuous casting operation in a certain temperature. For example, aslab reheating temperature (SRT) may be 1200° C. to 1400° C. When theSRT is less than 1200° C., the segregated components may not besufficiently re-used during casting, and thus, it may be difficult toobserve a large homogenization effect of alloying elements. Also, alarge solution effect of Ti may be difficult to be observed. Although ahigher SRT is beneficial to homogenization, when the SRT exceeds 1400°C., it is difficult to secure the strength of a steel plate (or ahot-stamping component) due to an increase in austenite grain size, andthe manufacturing cost of the steel plate may increase due to anexcessive heating operation.

In the hot-rolling operation of a steel slab S210, the reheated steelslab is hot-rolled at a certain finishing delivery temperature (FDT).For example, the FDT may be 880° C. to 950° C. At this time, when theFDT is less than 880° C., it may be difficult to secure workability of asteel plate as a duplex grain structure occurs due to abnormal regionrolling, and the workability of the steel plate is reduced due to unevenmicrostructures and as well as also mass flowing during hot-rolling mayoccur due to a rapid phase change. When the FDT exceeds 950° C.,austenite grains may become coarse. In addition, TiC precipitates becomecoarse, and the performance of a hot-stamping component may decrease.

In the cooling/coiling operation S220, the hot-rolled steel plate iscooled to a certain coiling temperature (CT) to be coiled. For example,the CT is 550° C. to 800° C. The CT affects the redistribution of C, andwhen the CT is less than 550° C., the low-temperature phase fraction dueto subcooling may increase, a rolling load may be deepened duringcold-rolling, and the ductility of the steel plate (or the hot-stampingcomponent) may rapidly decrease. On the other hand, when the CT exceeds800° C., deterioration in the moldability and strength of the steelplate (or the hot-stamping component) may occur due to abnormal graingrowth or excessive grain growth.

In the cold-rolling operation S230, the coiled steel plate is uncoiledto perform pickling, and then cold-rolled. At this time, pickling isperformed to remove the scale of the coiled steel plate, that is, thescale of a hot-rolled coil manufactured through the hot-rollingoperation described above.

The annealing heat treatment operation S240 is an operation ofperforming an annealing heat treatment on the cold-rolled steel plate ata temperature of 700° C. or higher. For example, the annealing heattreatment includes an operation of heating the cold-rolled steel plateand cooling the heated cold-rolled steel plate at a certain coolingrate.

The hot-dip plating operation S250 is an operation of forming a platedlayer on the annealed heat-treated steel plate. For example, in thehot-dip plating operation S250, an Al—Si plated layer 200 may be formedon the annealed heat-treated steel plate, that is, the base steel plate100.

In detail, in the hot-dip plating operation S250, the base steel plate100 may be immersed in a hot-dip plating bath including an amount of 8wt % to 12 wt % of Si and excess Al. At this time, the hot-dip platingbath may maintain a temperature of 400° C. to 700° C. The plated layer200 may be formed by plating at 40 g/m² to 80 g/m² on both surfaces ofthe base steel plate 100.

The oil coating operation S120 is an operation of coating a plated steelplate manufactured by immersing the base steel plate 100 in a platingbath including Al and Si with an oil including an ester-based compound.The oil may include an amount of 10 wt % to 30 wt % of hydrotreatedheavy paraffin refined oil, an amount of 30 wt % to 50 wt % ofsolvent-dewaxed heavy paraffin refined oil, an amount of 1 wt % to 5 wt% of solvent-refined heavy paraffin refined oil, and an amount of 10 wt% to 40 wt % of an ester-based compound. For example, the oil mayinclude an amount of 10 wt % to 30 wt % of hydrotreated heavy paraffinrefined oil, an amount of 30 wt % to 50 wt % of solvent-dewaxed heavyparaffin refined oil, an amount of 1 wt % to 5 wt % of solvent-refinedheavy paraffin refined oil, and an amount of 3 wt % to 40 wt % ofpolyester. An ester component may be included in the solvent-dewaxedheavy paraffin refined oil and the polyester. In another exemplaryembodiment, the oil may include an amount of 10 wt % to 30 wt % ofhydrotreated heavy paraffin refined oil, an amount of 30 wt % to 50 wt %of solvent-dewaxed heavy paraffin refined oil, an amount of 1 wt % to 5wt % of solvent-refined heavy paraffin refined oil, and an amount of 3wt % to 40 wt % of metal ester. The ester component may be included inthe solvent-dewaxed heavy paraffin refined oil and the metal ester. Inan embodiment, “FERROCOTE® 6130”, which is a commercial product ofQuaker, may be used as the oil.

In the oil coating operation S120, the plated steel plate may be coatedwith the oil at 0.1 g/m² to 10 g/m² on. An oil film may be formed on asurface of the Al—Si plated layer by coating the plated steel plate withthe oil at 0.1 g/m² to 10 g/m². The oil film formed on the surface ofthe Al—Si plated layer may not only affect a reaction between the basesteel plate 100 and the Al—Si plated layer when heating a blank to bedescribed below, but also reduce an amount of hydrogen flowing from theoutside to the base steel plate 100 when the blank is heated. When theplated steel plate is coated with an amount of oil less than 0.1 g/m², asurface of a component manufactured by the method of manufacturing ahot-stamping component may be corroded. On the other hand, when theplated steel plate is coated with the amount of oil exceeding 10 g/m², acoil may be deformed (bucklied) in a radial direction.

For example, a method of manufacturing a plated steel plate for hotstamping may include the plated steel plate manufacturing operation S110and the oil coating operation S120. A plated steel plate for hotstamping in which an oil is coated on the surface through the method ofmanufacturing a plated steel plate for hot stamping including the platedsteel plate manufacturing operation S110 and the oil coating operationS120 may be manufactured.

The blank forming operation S130 is an operation of forming a blank bycutting the plated steel plated on which an oil is coated. In the blankforming operation S130, a blank may be formed by cutting the platedsteel plated in which an oil is coated on the surface into a desiredshape according to a purpose. A blank for hot stamping may be providedby cutting the plated steel plate in which an oil is coated on thesurface.

For example, the oil coating operation S120 may be performed after theblank forming operation S130 is performed. In this case, in the blankforming operation S130, a blank may be formed by cutting the platedsteel plate into a desired shape according to a purpose. In addition, inthe oil coating operation S120, the blank formed through the blankforming operation S130 may be coated with an oil including anester-based compound. In the oil coating operation S120, the oil may becoated at about 0.1 g/m² to about 10 g/m² on the blank.

The blank heating operation S140 may be an operation of heating the cutblank in a heating furnace. In detail, the blank heating operation S140may be an operation of heating the cut blank in the heating furnacemaintained at 800° C. to 1000° C.

For example, when the oil coating operation S120 is performed after theblank forming operation S130 is performed, the blank heating operationS140 may be an operation of heating a blank on which an oil is coated ina heating furnace. In detail, the blank heating operation S140 may be anoperation of heating a blank, on which the blank forming operation S130and the oil coating operation S120 are sequentially performed, in aheating furnace maintained at 800° C. to 1000° C.

For example, the blank heating operation S140 may include a step heatingoperation and a soaking operation. In the step heating operation, theblank may be heated in stages, and in the soaking operation, the blankmay be soaked at a uniform temperature. In detail, in the step heatingoperation, as the blank passes through a plurality of sections providedin the heating furnace, the temperature of the blank may be raised instages. There may be a plurality of sections in which the step heatingoperation is performed, among the plurality of sections provided in theheating furnace, and the temperature is set for each section so as toincrease in a direction from an inlet of the heating furnace into whichthe blank is inserted to an outlet of the heating furnace from which theblank is discharged, and thus the temperature of the blank may be raisedin stages. The soaking operation may be performed after the step heatingoperation. In the soaking operation, the stepwise heated blank may beheat-treated while passing through a section of the heating furnace setas a temperature of Ac3 to 1000° C. Preferably, in the soakingoperation, the stepwise heated blank may be soaked at a temperature of930° C. to 1000° C. More preferably, in the soaking operation, thestepwise heated blank may be soaked at a temperature of 950° C. to 1000°C. Also, among the plurality of sections provided in the heatingfurnace, there may be at least one section in which the soakingoperation is performed.

FIG. 5 is a diagram for explaining a heating furnace having a pluralityof sections in the blank heating operation of the method ofmanufacturing a hot-stamping component according to an exemplaryembodiment of the present disclosure.

Referring to FIG. 5 , the heating furnace according to an exemplaryembodiment may include a plurality of sections with differenttemperature ranges. In more detail, the heating furnace may include afirst section P₁ having a first temperature range T₁, a second sectionP₂ having a second temperature range T₂, a third section P₃ having athird temperature range T₃, a fourth section P₄ having a fourthtemperature range T₄, a fifth section P₅ having a fifth temperaturerange T₅, a sixth section P₆ having a sixth temperature range T₆, and aseventh section P₇ having a seventh temperature range T₇.

For example, in the step heating operation of the blank heatingoperation S140, a blank may be stepwise heated in stages while passingthrough a plurality of sections (for example, the first section P₁ tothe fourth section P₄) defined in the heating furnace. In addition, inthe soaking operation of the blank heating operation S140, the blankstepwise heated in the first section P₁ to the fourth section P₄ may besoaked in the fifth section P₅ to the seventh section P₇.

The first to seventh sections P₁ to P₇ may be sequentially arranged inthe heating furnace. The first section P₁ having the first temperaturerange T₁ may be adjacent to an inlet of the heating furnace into whichthe blank is inserted, and the seventh section P₇ having the seventhtemperature range T₇ may be adjacent to an outlet of the heating furnacefrom which the blank is discharged. Accordingly, the first section P₁having the first temperature range T₁ may be a first section of theheating furnace, and the seventh section P₇ having the seventhtemperature range T₇ may be a last section of the heating furnace. Thefifth section P₅, the sixth section P₆, and the seventh section P₇ amongthe plurality sections of the heating furnace, may not be sections inwhich step heating is performed, but rather be sections in which soakingis performed.

Temperatures of the plurality of sections provided in the heatingfurnace, for example, temperatures of the first to seventh sections P₁to P₇, may increase in a direction from the inlet of the heating furnaceinto which the blank is inserted to the outlet of the heating furnacefrom which the blank is discharged. However, temperatures of the fifthsection P₅, the sixth section P₆, and the seventh section P₇ may be thesame. Also, a difference in temperature between two adjacent sections,among the plurality of sections provided in the heating furnace, may begreater than 0° C. and less than or equal to 100° C. For example, adifference in temperature between the first section P₁ and the secondsection P₂ may be greater than 0° C. and less than or equal to 100° C.

For example, the first temperature range T₁ of the first section P₁ maybe 840° C. to 860° C., or 835° C. to 865° C. The second temperaturerange T₂ of the second section P₂ may be 870° C. to 890° C., or 865° C.to 895° C. The third temperature range T₃ of the third section P₃ may be900° C. to 920° C., or 895° C. to 925° C. The fourth temperature rangeT₄ of the fourth section P₄ may be 920° C. to 940° C., or 915° C. to945° C. The fifth temperature range T₅ of the fifth section P₅ may beAc3 to 1000° C. Preferably, the fifth temperature range T₅ of the fifthsection P₅ may be 930° C. or more and 1000° C. or less. More preferably,the fifth temperature range T₅ of the fifth section P₅ may be 950° C. ormore to 1000° C. or less. The sixth temperature range T₆ of the sixthsection P₆ and the seventh temperature range T₇ of the seventh sectionP₇ may be the same as the fifth temperature range T₅ of the fifthsection P₅.

Although it is shown in FIG. 5 that the heating furnace according to anexemplary embodiment includes seven sections with different temperatureranges from each other, the present disclosure is not limited thereto.Five, six, or eight sections with different temperature ranges from eachother may be provided in the heating furnace.

For example, the blank may be soaked after being stepwise heated. Thesoaking of the blank may be performed in the last portion among theplurality of sections provided in the heating furnace, and may beperformed at a temperature of Ac3 to 1000° C.

The soaking operation may be performed in the last portion among theplurality of sections of the heating furnace. For example, the soakingoperation may be performed in the fifth section P₅, the sixth sectionP₆, and the seventh section P₇ of the heating furnace. When a pluralityof sections are provided in the heating furnace and a length of onesection is long, there may be a problem such as a change in temperaturewithin the section. Accordingly, the section in which the soakingoperation is performed may be divided into the fifth section P₅, thesixth section P₆, and the seventh section P₇, and the fifth section P₅,the sixth section P₆, and the seventh section P₇ may have the sametemperature range in the heating furnace.

In the soaking operation, the stepwise heated blank may be soaked at atemperature of Ac3 to 1000° C. Preferably, in the soaking operation, thestepwise heated blank may be soaked at a temperature of 930° C. to 1000°C. More preferably, in the soaking operation, the stepwise heated blankmay be soaked at a temperature of 950° C. to 1000° C.

For example, a ratio of a length D₁ of a section for step heating theblank to a length D₂ of a section for soaking the blank may be 1:1 to4:1. In more detail, a ratio of a sum of lengths of the first section P₁to the fourth section P₄, which are sections for step heating the blank,to a sum of lengths of the fifth section P₅ to the seventh section P₇,which are sections for soaking the blank, may satisfy 1:1 to 4:1. Whenthe length of the section for soaking the blank increases, so that theratio of the length D₁ of the section for step heating the blank to thelength D₂ of the section for soaking the blank is greater than 1:1, anaustenite (FCC) structure is generated in the soaking section, which mayincrease an amount of hydrogen permeated into the blank, therebyincreasing the risk of delayed fracture. Also, when the length of thesection for soaking the blank decreases, so that the ratio of the lengthD₁ of the section for step heating the blank to the length D₂ of thesection for soaking the blank is less than 4:1, sufficient sections(periods of time) for soaking are not secured, and thus the strength ofa component manufactured by the method of manufacturing a hot-stampingcomponent may be uneven.

For example, the soaking section among the plurality of sectionsprovided in the heating furnace may have a length of 20% to 50% of thetotal length of the heating furnace.

In addition, in the blank heating operation S140, at least two blankshaving different thicknesses from each other may be simultaneouslytransferred into the heating furnace.

For example, the blank may remain in the heating furnace for 180 secondsto 500 seconds. In more detail, a period of time for step heating theblank and soaking the blank in the heating furnace may be 180 seconds to500 seconds. When the period of time for the blank to remain in theheating furnace is less than 180 seconds, it may be difficult for theblank to be sufficiently soaked at a desired temperature. Also, when theperiod of time for the blank to remain in the heating furnace is morethan 500 seconds, an amount of hydrogen permeated into the blankincreases, thereby leading to an increased risk of delayed fracture anddeterioration in corrosion resistance after a hot stamping operation.

FIG. 6 is a graph showing a change in temperature over time of a blankcoated with an oil including an ester-based compound and a blank coatedwith a general oil.

Referring to FIG. 6 , although a substantially the same heating ratefrom room temperature to 600° C. is shown in cases of a blank 310 coatedwith an oil including an ester-based compound and a blank 320 coatedwith a general oil, it can be seen that the heating rate of the blank310 coated with the oil including the ester-based compound was fasterthan the heating rate of the blank 320 coated with the general oil at atemperature of 600° C. to 900° C. That is, it can be seen that theheating rate of the blank 310 coated with the oil including an amount of10 wt % to 40 wt % of the ester-based compound was faster than theheating rate of the blank 320 coated with the general oil.

A hydrolysis reaction of the ester-based compound occurs in a section ofwhich the temperature of the blank is 600° C. to 900° C. The hydrolysisreaction of the ester-based compound is an endothermic reaction, and thetemperature of the heating furnace in the corresponding section isincreased to promote the hydrolysis reaction, so that the inflow ofhydrogen into the blank may be blocked, and the plated layer 200including the first layer 210, the second layer 220, and theisland-shaped intermetallic compound portion 230 in the second layer 220may be formed on the base steel plate 100, as described in FIG. 1 . Atthis time, an average heating rate of a blank in a section at atemperature of 600° C. to 900° C. of the blank 310 coated with an oilincluding 10 wt % to 40 wt % of the ester-based compound may be about4.5° C./s to about 10° C./s.

For example, the oil may include an amount of 10 wt % to 40 wt % of theester-based compound. As an amount of 10 wt % to 40 wt % of theester-based compound is included in the oil, an amount of diffusiblehydrogen may be decreased to improve the hydrogen delayed fractureperformance, and a dense oxide film may be formed by the hydrolysisreaction of the ester-based compound. When the oil includes less than 10wt % of the ester-based compound, the amount of diffusible hydrogen mayincrease, and hydrogen delayed fracture may occur. On the other hand,when the oil includes greater than 40 wt % of the ester-based compound,stains may exist on a surface of a component manufactured by the methodof manufacturing the hot-stamping component.

The blank transferring operation S150 is an operation of transferringthe heated blank from the heating furnace to a press mold. In the blanktransferring operation S150, the heated blank may be air-cooled for 10seconds to 15 seconds.

The molded body forming operation S160 is an operation of forming amolded body by hot-stamping the transferred blank. The molded bodycooling operation S170 is an operation of cooling the formed moldedbody.

A final product may be formed by cooling the molded body at the sametime as molding the molded body into a final component shape. A coolingchannel through which a refrigerant circulates may be provided in thepress mold. The heated blank may be rapidly cooled by circulation of therefrigerant supplied through the cooling channel provided in the pressmold. In this regard, in order to prevent a spring back phenomenon andmaintain a desired shape of a plate material, the blank may be pressedand rapidly cooled while the press mold is closed. When molding andcooling the heated blank, the blank may be cooled with an averagecooling rate of at least 10° C./s to a martensite end temperature. Theblank may be held in the press mold for about 3 seconds to about 20seconds. When a period of time for the blank being held in the pressmold is less than 3 seconds, cooling of a material is not sufficientlyperformed, and thus temperature variation of each portion due toresidual heat may affect embrittlement quality. In addition, because asufficient amount of martensite is not generated, mechanical propertiesmay not be secured. On the other hand, when the period of time for theblank being held in the press mold is more than 20 seconds, the timebeing held in the press mold may be increased, thereby causing lowerproductivity.

A hot-stamping component (member) having delayed fracture performancemay be formed by applying the above-stated composition and operationconditions. The microstructure of a base layer of the hot-stampingcomponent may have a full-martensite structure, and may satisfy a yieldstrength of 900 MPa or more, a tensile strength of 1350 MPa or more, anelongation rate of 5% or more.

Hereinafter, the present disclosure will be described in more detailthrough embodiments. However, the following embodiments are forexplaining the present disclosure in more detail, and the scope of thepresent disclosure is not limited to the following embodiments. Numerousmodifications and adaptations will be readily apparent to one ofordinary skill in the art without departing from the spirit and scope.

TABLE 1 Component (wt %) C Si Mn P S Cr Ti B Composition 1 0.23 0.241.17 0.014 0.002 0.17 0.03  0.002 Composition 2 0.29 0.21 1.39 0.01 0.001 0.19 0.031 0.002

TABLE 2 Whether Retention Step Soaking in Heating Tem- Heating hasperature Furnace Composition Oil Performed (° C.) Time (s) EmbodimentComposition 1 Oil 1 ◯ 950 300 1 Embodiment Composition 1 Oil 1 ◯ 950 4202 Embodiment Composition 2 Oil 1 ◯ 900 300 3 Comparative Composition 1Oil 2 ◯ 950 300 Example 1 Comparative Composition 1 Oil 2 ◯ 950 420Example 2 Comparative Composition 2 Oil 2 ◯ 900 300 Example 3Comparative Composition 1 Oil 1 X 950 300 Example 4 ComparativeComposition 2 Oil 1 X 900 420 Example 5

Table 1 is a table showing a composition of a base steel plate accordingto an exemplary experimental embodiment of the present disclosure, andTable 2 is a table showing steel plate compositions, oil conditions,cases whether step heating has performed, soaking temperatures, andretention time in a heating furnace for manufacturing a hot-stampingcomponent according to an exemplary experimental embodiment of thepresent disclosure.

The composition 1 of Table 1 was set for a tensile strength of 1350 MPaor more as a target, and the composition 2 was set for a tensilestrength of 1680 MPa or more as a target.

Referring to Tables 1 and 2, steel materials of Embodiments 1 and 2, andComparative Examples 1, 2, and 4 may include a composition ofcomposition 1 in Table 1 and excess Fe, and steel materials ofEmbodiment 3, and Comparative Examples 3 and 5 may have a composition ofcomposition 2 and excess Fe. Hot-rolling, cooling/coiling, cold-rolling,an annealing heat treatment, and a hot-dip plating treatment wereperformed on the steel materials having compositions of Embodiments 1 to3, and Comparative Examples 1 to 5.

In the cases of Embodiments 1 to 3, and Comparative Examples 4 and 5, anoil film was formed by coating a surface of an Al—Si plated layer with0.1 g/m² of oil 1. In the cases of Comparative Examples 1 to 3, an oilfilm was formed by coating the surface of the Al—Si plated layer with0.1 g/m² of oil 2. At this time, a “Ferrocote 6130” product of Quakerwas used as the oil 1, and “BW-80HG”, which is a commercial product ofBuhmwoo, was used as the oil 2. The oil 1 includes 10 wt % to 40 wt % ofpolyester, but the oil 2 includes less than 10 wt % of ester-basedcompounds.

Subsequently, blanks of Embodiments 1 to 3, in which the oil 1 wascoated on surfaces, and blanks of Comparative Examples 1 to 3, in whichthe oil 2 was coated on surfaces, were heated according to theconditions in Table 2, and the heated blanks were transferred to amolding mold to perform press molding and cooled at a cooling rate of10° C./s or greater, thereby manufacturing hot-stamping components. Inaddition, blanks of Comparative Examples 4 and 5, in which the oil 1 wascoated on surfaces, were heated (single-heated) at a uniform temperatureaccording to the conditions in Table 2, and the heated blanks weretransferred to the molding mold to perform press molding and cooled at acooling rate of 10° C./s or greater, thereby manufacturing hot-stampingcomponents. Single-heated means heating the blank at a constanttemperature.

<Tensile Strength Test>

After manufacturing the hot-stamping components of Embodiments 1 to 3,and Comparative Examples 1 to 5 of Table 3, a yield strength, a tensilestrength, and an elongation rate at room temperature were measured.

TABLE 3 Material Characteristics Yield Strength Tensile StrengthElongation (MPa) (MPa) Rate (%) Embodiment 1  908 1413 8.3 Embodiment 2 912 1432 8.1 Embodiment 3 1058 1713 7.3 Comparative  905 1409 8.1Example 1 Comparative  910 1428 8.0 Example 2 Comparative 1031 1704 7.1Example 3 Comparative  901 1356 8.2 Example 4 Comparative 1027 1684 7.2Example 5

Table 3 is a table showing the yield strength, tensile strength, andelongation rate at room temperature of Embodiments 1 to 3, andComparative Examples 1 to 5. Referring to Table 4, it can be seen thatin the cases of Embodiments 1 and 2, the yield strength was 900 MPa ormore, the tensile strength was 1350 MPa or more, and the elongation ratewas 5% or more. In addition, it can be seen that in the case ofEmbodiment 3, the tensile strength was 1680 MPa or more and the yieldstrength was 1000 MPa or more.

Accordingly, even when a hot-stamping component is manufactured by ablank in which an oil (oil 1) including about 10 wt % to about 40 wt %of ester-based compounds is coated on a plated layer, the hot-stampingcomponent may have a tensile strength greater than or equal to a presettarget (for example, 1350 MPa or 1680 MPa).

<Evaluation of an Amount of Diffusible Hydrogen and Hydrogen DelayedFracture Characteristic>

Thermal desorption spectroscopy was performed on Embodiments 1 to 3, andComparative Examples 1 to 5. In detail, an amount of diffusible hydrogenemitted from the hot-stamping component was measured under 350° C. orless, while raising the temperature form room temperature to 500° C. ata heating rate of 20° C./min. In addition, evaluation of hydrogendelayed fracture was conducted on Embodiments 1 to 3, and ComparativeExamples of 1 to 5. The evaluation of the hydrogen delayed fracture wasperformed by a four-point bending test. The four-point bending test is atest method for checking whether stress corrosion cracking occurs byapplying a stress having a level below an elastic limit at a particularpoint of a specimen manufactured by reproducing a state exposed to acorrosive environment. At this time, stress corrosion cracking refers toa crack that occurs when corrosion and continuous tensile stress actsimultaneously.

In detail, a stress of 1000 MPa in air was applied on each sample inEmbodiments 1 and 2, and Comparative Examples 1 and 2, which had atensile strength of 1350 MPa or more, for 100 hours to check whether afracture occurs. In addition, a stress of 1200 MPa in air was applied toeach sample in Embodiment 3, and Comparative Examples 3 and 4, which hada tensile strength of 1680 MPa, for 100 hours to check whether afracture occurs.

TABLE 4 Amount of Diffusible Hydrgen Hydrogen Delayed (wppm) FractureEmbodiment 1 0.41 Non-fractured Embodiment 2 0.46 Non-fracturedEmbodiment 3 0.346 Non-fractured Comparative Example 1 0.66 FracturedComparative Example 2 0.92 Fractured Comparative Example 3 0.528Fractured Comparative Example 4 0.79 Fractured Comparative Example 50.61 Fractured

FIGS. 7A to 7C are graphs respectively showing heating degassinganalysis results of Embodiment 1 and Comparative Example 1, Embodiment 2and Comparative Example 2, and Embodiment 3 and Comparative Example 3,and Table 4 is a table showing an amount of diffusible hydrogen emittedfrom Embodiments 1 to 3, and Comparative Examples 1 to 5, and anevaluation result of hydrogen delayed fracture.

Referring to FIG. 7A and Table 4, it can be seen that at a temperatureof 300° C. or less, an amount of diffusible hydrogen emitted fromEmbodiment 1 was less than an amount of diffusible hydrogen emitted fromComparative Example 1. Also, according to an evaluation result ofhydrogen delayed fracture, fracture did not occur in Embodiment 1, butfracture occurred in Comparative Example 1.

Referring to FIG. 7B and Table 4, it can be seen that at a temperatureof 300° C. or less, an amount of diffusible hydrogen emitted fromEmbodiment 2 was less than an amount of diffusible hydrogen emitted fromComparative Example 2. Also, according to an evaluation result ofhydrogen delayed fracture, fracture did not occur in Embodiment 2, butfracture occurred in Comparative Example 2.

Referring to FIG. 7C and Table 4, it can be seen that at a temperatureof 300° C. or less, an amount of diffusible hydrogen emitted fromEmbodiment 3 was less than an amount of diffusible hydrogen emitted fromComparative Example 3. Also, according to an evaluation result ofhydrogen delayed fracture, fracture did not occur in Embodiment 3, butfracture occurred in Comparative Example 3.

Accordingly, when a surface of a plated layer is coated with an oil (oil1) including an ester-based compound, an amount of hydrogen inflow fromthe outside may decrease, and thus, the resistance against delayedhydrogen fracture was excellent.

In addition, an amount of diffusible hydrogen emitted from each ofEmbodiments 1 and 3, on which stepwise heating was performed, was lessthan an amount of diffusible hydrogen emitted from each of ComparativeExamples 4 and 5, on which single-heating was performed, and accordingto the evaluation result of hydrogen delayed fracture, fracture did notoccur in Embodiments 1 and 3, but fracture occurred in ComparativeExamples 4 and 5.

Accordingly, as compared with a case of performing single-heating, inthe case of performing step heating, the amount of hydrogen inflow wasreduced, and thus, the resistance against hydrogen delayed fracture wasexcellent.

<Observation of Thickness of Surface Layer>

FIGS. 8A and 8B are photographs respectively showing a surface layer ofEmbodiment 1 and Comparative Example 1. FIGS. 8A and 8B are diagramsshowing results of measuring cross sections of Embodiment 1 andComparative Example 1 by a transmission electron microscope (TEM).

Referring to FIGS. 8A and 8B, a thickness of the surface layer 240 ofEmbodiment 1 was about 165 nm, and a thickness of a first surface area450 of Comparative Example 1 was about 92 nm. Accordingly, Embodiment 1had a surface layer having a thickness greater than that of ComparativeExample 1, and it is determined that the difference in thickness wascaused by a difference in heating rates of the blank in Embodiment 1 andthe blank of Comparative Example 1, as shown in FIG. 6 . Because thesurface layer 240 of Embodiment was formed thicker than the surfacelayer 450 of Comparative Example 1, the base steel plate 100 may be moreeffectively prevented from being oxidized when a plated layer is coatedwith an oil (oil 1) including an ester-based compound.

<Weldability Evaluation>

Weldability evaluation was conducted on Embodiment 1 and ComparativeExample 1. In the weldability evaluation, a 6 mm welding tip was appliedto a welding portion with a pressing force of 350 kgf for 4 minutes at930° C., and contact resistance was measured in a state of applying acurrent.

FIG. 9 is a graph showing resistance measurement results during spotwelding of Embodiment 1 and Comparative Example 1.

Referring to FIG. 9 , it can be seen that a contact resistance ofEmbodiment 1 was less than a contact resistance of ComparativeExample 1. In particular, it can be seen that the contact resistance ofEmbodiment 1 in about 5 ms during an initial welding period was lessthan the contact resistance of Comparative Example 1. Accordingly,because the contact resistance of Embodiment 1 was less than the contactresistance of Comparative Example 1, it can be confirmed that ahot-stamping component of Embodiment 1 had excellent weldabilitycompared to a hot-stamping component of Comparative Example 1.

<Corrosion Resistance Evaluation>

Corrosion Evaluation was conducted on the hot-stamping components ofEmbodiment 1 and Comparative Example 1. In the corrosion evaluation, athree-electrode electrochemical cell was constructed by using a workingelectrode as a specimen, a high-purity carbon rod as a counterelectrode, a saturated calomel electrode as a reference electrode, tocarry out a copper potential polarization test. The copper potentialpolarization test was carried out after verifying electrochemicalstabilization by measuring an open-circuit potential (OCP) in a 3.5%sodium chloride (NaCl) solution for 10 hours, and a potential from about−250 mVSCE to about 0 mVSCE based on a corrosion potential (Ecorr) wasapplied at a scanning rate of 0.166 mV/s.

FIG. 10 is a graph showing corrosion evaluation experiment results ofEmbodiment 1 and Comparative Example 1. The graph of FIG. 10 iscorrosion current measurement results of Embodiment 1 and ComparativeExample 1, and a corrosion current is a value corresponding to a currentdensity at a time when a branch of a stably maintained potential occurs.

Referring to FIG. 10 , a corrosion current of Embodiment 1 was measuredas 5×10⁻⁴ A, and a corrosion current of Comparative Example 1 wasmeasured as 5×10⁻⁴ A. Accordingly, it can be seen that a current densityrelated to corrosion of Embodiment 1 was less than a current densityrelated to corrosion of Comparative Example 1. Therefore, it can beconfirmed that the corrosion resistance of Example 1 was superior tothat of Comparative Example 1.

According to exemplary embodiments of the present disclosure, a blankcoated with an oil including an ester-based compound may be hot-stampedto improve the hydrogen embrittlement, corrosion resistance, andweldability of a component manufactured by hot stamping.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments. While one or more embodiments have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thedisclosure as defined by the following claims.

What is claimed is:
 1. A method of manufacturing a hot-stampingcomponent, the method comprising: manufacturing a plated steel plate byimmersing a base steel plate in a plating bath comprising aluminum andsilicon; coating the plated steel plate with an oil comprising anester-based compound; forming a blank by cutting the plated steel platecoated with the oil; and heating the blank in a heating furnace, whereinthe oil comprises an amount of 10 wt % to 30 wt % of hydrotreated heavyparaffin refined oil, an amount of 30 wt % to 50 wt % of solvent-dewaxedheavy paraffin refined oil, an amount of 1 wt % to 5 wt % ofsolvent-refined heavy paraffin refined oil, and an amount of 10 wt % to40 wt % of an ester-based compound.
 2. The method of claim 1, whereinthe oil is coated at 0.1 g/m² to 10 g/m² on the plated steel plate. 3.The method of claim 1, wherein in the heating of the blank in theheating furnace, the heating furnace has a plurality of sections havingdifferent temperature ranges from each other, and the blank is heated instages in the heating furnace.
 4. The method of claim 3, wherein in theheating of the blank in the heating furnace, at least two blanks havingdifferent thicknesses from each other are simultaneously transferredinto the heating furnace.
 5. The method of claim 1, further comprising,after the heating of the blank, transferring the heated blank from theheating furnace to a press mold; forming a molded body by hot-stampingthe transferred blank; and cooling the formed molded body.